The invention relates to a method for illuminating flat bar codes, an image of the bar code being generated on a receiving sensor via receiver optics for the recognition and evaluation of the bar code. The illumination and the receiving sensor are matched to the usually longitudinally extended flat form of a bar code. The method is suitable for use in a bar code reader.
In semiconductor production, semiconductor structures (electronic components; chips) are constructed on silicon wafers, using different chemical and physical processes. During the entire chip production, the wafers must always be able to be assigned unequivocally to a production order. Only in this way can the next process step for the wafers be determined reliably and the process data arising can be stored. For the unequivocal identification of various wafers, a marking is applied to the latter. For marking, laser methods can be used in an advantageous way. Here, either a so-called clear text and/or a bar code marking is applied to a wafer. Because of the multiplicity of successive process steps, in which material coatings, etching sequences or the like are carried out on the wafer, the marking is affected detrimentally. The marking quality decreases on average with the number of production steps.
If the guiding of the process is to be supported by the use of automatic identification devices, even markings of poor quality must be able to be identified reliably.
The identification of wafers proves to be very difficult, because of the disturbing variables present and the treatment processes to be carried out, which affect the markings detrimentally. The identification is therefore often carried out by humans. In individual cases, intelligent image processing systems or scanners especially adapted to this problem are also used for bar code recognition. Disturbing variables occurring such as, for example, inaccurate wafer feeding, tilting of the wafer and streaks on the marking or contrasts which are too low within the bar code lead to a reduced operational reliability of the identification systems. The recognition of the marking with the human eye is cost-intensive and time-intensive. The use of image processing systems is likewise costly and not sufficiently reliable. The recognition times, as a rule, are over one second.
In German Patent Specification DE 27 04 983 C3, a device is described with which the whole field of view, for example the field of the marking area of a bar code, is imaged onto the effective area of a row of photodiodes used as receiving sensor. However, the device is used for the recognition of faults in the surface or in the dimensions of an object.